The present invention relates to a media drive that exchanges a command and transfer data with a host by means of serial communications, and to a power saving method thereof. The present invention, in particular, relates to a media drive that is intended for reduction in power consumption in serial communications, and to a power saving method thereof.
Devices using various types of media such as optical disks and magnetic tapes are known as information recording and reproducing devices. Among them, hard disk drives (hereinafter referred to as “HDD”) have become popular as storage devices for computers to such an extent that they are one of the storage devices indispensable for today's computer systems. Further, not limited to computers, their application is widening more and more due to the superior characteristics with the advent of moving picture recording/reproducing devices, car navigation systems, removable memories for digital cameras and so on.
From the viewpoint of the environmental protection, the long-time operation of portable devices with built-in power supply, or the like, it is necessary to further reduce the power consumption of external storage devices such as a HDD. For example, with the object of reducing the power consumption, besides an “Active” mode in which no operation for power saving is performed, HDDs are usually provided with a plurality of power save modes including an “Idle” mode in which no read and write operations are performed but track following, and a “Standby” mode in which a spindle motor for rotating a disk is stopped so that the power consumption is reduced. For example, during the non-operating period, during which no command is received from the host, the devices are brought into these power save modes so as to reduce the power consumption (refer to a patent document 1 (Japanese Patent Laid-Open No. 2000-173152)).
Incidentally, almost all of HDDs, which are built into personal computers (PC) excluding servers and some workstations, adopt ATA (AT Attachment) or IDE (Integrated Drive Electronics) interface. In addition, as a result of the improvement in performance and increase in capacity of the ATA interface, even entry servers adopt ATA as a hard disk interface in recent years because costs of both a drive and a controller are low as compared with costs when SCSI (small computer system interface) is adopted. It is to be desired that a further improvement in performance be achieved without losing advantages of ATA, one of which is very low cost in contrast to the expensive SCSI interface.
As one method for achieving the improvement in performance, instead of the transmission method by means of the conventional parallel transmission, the serial transmission method is proposed to speed up the exchange of data with a host. The serial transmission has a feature advantageous to speedup. More specifically, as compared with the parallel transmission, the number of signal lines dramatically decreases, and accordingly less interference occurs between signal lines as compared with the parallel transmission. Standards of this Serial ATA (hereinafter referred to as “SATA”) are being defined by Serial ATA Working Group constituted of, for example, main hard disk vendors.
In the SATA II (Non-patent literature 1 (“Serial ATA II: Extensions to Serial ATA 1.0a” [searched on Nov. 1, 2004] Internet<URL: http://www.serialata.org/specifications.asp>)), a command queuing technology called NCQ (Native Command Queuing) is adopted to achieve a further improvement in performance. The NCQ permits a HDD itself to internally determine the execution order of commands that are queued. This makes it possible to effectively reduce the sum of the seek time and the rotational latency, which is influenced by the mechanical internal operation of the HDD.